Apparatus for sequentially keying and connecting a plurality of oscillators to a common output circuit



19484 R. F. WILD ETAL I 2,457,790

APPARATUS FOR SEQUENTIALLY. KEYING AND CONNECTING A PLURALITY OFOSCILLATORS TO A COMMON OUTPUT CIRCUIT Filed 001: 6, 1945 4 Sheets-Sheetl AAAAAAAA vvv vvvv In I INVENTOR. RUDOLF F. wu 0 FRED J. CURRANATTORNEY.

R. F. WILD ET AL v APPARATUS FOR SEQUENTIALLY KEYING AND CONNECTING APLURALITY OF OSCILLATORS TO A COMMON OUTPUT CIRCUIT Dec. 28, 1948.

4 Sheets-Sheet 2 Filed Oct 6 1945 AT TOR N EY.

R. F. WILD ET AL APPARATUS FOR SEQUENTIALLY KEYING AND Dec. 28, 1948.

' CONNECTING A PLURALITY 0F OSCILLATORS TO A COMMON OUTPUT CIRCUIT 4 Sheets-Sheet 3 Filed Oct. 6, 1945 INVENTOR. RUDOLF F. WILD BY FRED J.CURRAN ATTORNEY.

Dec. 28, 1948.

R. F. WILD EFAL APPARATUS FOR SEQUENTIALLY KEYING AND CONNECTING APLURALITY -OF OSCILLATORS I TO A COMMON OUTPUT CIRCUIT Fild Oct. 6, 1945FIG. 4

4 Sheets-Sheet 4 FREQUENCY HIGH FREQUENCY LOW V0 LTA 6 E TIME OSCILLATORn SIGNAL II IIIIIIIIIIIIIIIIIIIIIIIIIII III I IIIII IIIII III II IIIIOSCILLATOR I2 SIGNAL (a) INPUT TO RECEIVER (0m) INPUT TO RECEIVER (dJA-COMPONENT OF DISCRIMINATOR OUTPUT u U .3 g A A A V V V V V V I (b) INPUTTo DISCRIMINATOR (BU INPUT T0 DISCRIMINATOR 5 5 5 9 I I I I I 9 I TIME IL I I I DISCRIMINATOR OUTPUT DISCRIHINATOR OUTPUT U1 DJ (9 (D E E 9 2TIME TIME (debA- COMPONENT OF DISCRIMINATOR OUTPUT INVENTOR. RUDOLF F.WILD FRED J.CURR'AN ATTORNEY.

Patented Dec. 28, 1948 AND (IQNNBGWL A) E QS:- GILLABQRS m. At COMMONvQU R 'D' CIR:-

CUIT

Rudolf F; wilfl 'andiFl-ed J. Gurmn, Philadelphia, Pa., assignors v toThe Brown; lnstnumentiGom-r pa v; P i adelphia m om mtinnzof P nn.-

sylvania Anolicationociobex 6, Se ialiNo. 620,82

The present invention relates to improvements:

inelectrioal' systems; and more especially; to electrical systemsfortransi'nitting. intelligence from a transmitting station to one or moreseparate.

and" remotely located receiving stations.

An object of the invention. is to provide im; movements in electricalsystems whereby an elec tron discharge device may simultaneously, servethe dual function of keying or intermittently blocking one oscillationenerator while, amplifying the oscillating output signalof. asecondoscil: lation generator.

Another object. of. the invention. is. toIJlKQJ/ide. improvements, inelectrical telautograph, systems, to the. end. that a combination offrequencifisbi two. electrical. signals. representative, of the, instelligenceto be transmitted, may be amplified by the same amplifier.and. transmitted. to. the remote receiving station. or. stations overthelsame transmission circuit. To, this end;. means. are provided at thereceiving station or stations as. Well as at thetransniittingstation forseparating; the electrical signals received. and; forutilizing. thornautomatically to adjust. areceiver. exhibit;

ing element in accordance with the intelligenceunoler transmission.

Considered. in its more: specific. aspects. the 111+ vention relates totransmission systems; of the.

type in which 'the-pGSlI/mn,Of'wpOintl/QM53215 mitted is conerectangular or polar coordinates, des lifim. When rectangularcoordinates. are employed. the position of the point to be transmitted;i013 83w ample is considered in; terms of. distance between the pointand: eachot two mutually penpendicue lar lines comprising the coordinateaxes, If the magnitude of the deviation in. position of; the

point from each of the coordinate axes is-transs mitted to. a remotelylocated receiving station, the

two deviations can be combined at the remotecillating electricalcurrents each corresponding in frequency to one coordinate of ainarkijngelee ment at the transmitter. Both high, frequencx signals. areamplified, by the same, amplifien and are transmitted by. the sametransmission cit. wit to. the remotely located receiving: station ered;in. terms; of the position: of; that point with. respect to; a pairotcoordinate; axes. The coordinates employed may be; either- 2. whereavmas-king.- ele ment; isv positioned; in; each coordinate according tothefrequency of: thecoij responding received signals; thereby; reproducingthechanges 01? position. of theimarl zing; element. at thetransmitter;

It is; a specific object of; theinvention, there: fore, to. provide.improvements in. electrical; tel.- autograph system to the end that thehigh fre.. quency signals. representative of? the position. of. the:marking element at; theitransmitten may. be amplified by a commonamplifier and; transmitted over 31.00MB transmission. cincuit. totheremote reoeivings-tation on stations. It isaspeoifioobv. i801 also; to.providein. conjunction with. such. transmission apparatus; means at: theremotely. located receiving stations or. stations. for separat-..ingthehigh frequency signals received: and. for utilizing: themtotadjostautomatioallyl a receiver marking element to apositioncorresponding to. theposition of? the transmitter' marking element;

The various. features of novelty. which charam. terioeour-inventiontarepointed outwith particmlarity in the claims annexed to and forming a Hpart of this specification. abetter under-.

standingoi the invention, however, itsadvantages, ancl specificobg'ectsattained by its use,- retjeltence shouldbe haci to theaccompanying; drawings and descriptive matterin which we haveillustrated and described preferred embodi' merits of the invention.

0i thedrawi-ngs:

Fig l illustratesawiring-diagramofthe-transmittee mechanism ofapre-ferred embodiment of our invention 2 illustrates a wiring diagramof a preferred form oi receiver mechanism which, may be employedinconnection with the transmission mechanism ot'Fig. 1;

Fig. 3* illustrates a modification of" the transmittermechanism,of'liig, 1'; and;

Fig. 4 shows voltagediagrains illustrating the operation of' theapparatus of Figs. 1;. and

In Fig; 1 there is illustrated a transmitter en bodying the principlesof our invention for producing two separate variable frequency highfrequency oscillating currents, each corresponding i fr quency t he evati n. of a. m rk ng. element from momutuallv p rp ndicu ar. i es 0.1;oordinate. a s whi h hav een esigna ed. b thererf rence cha a ers 2. and3.. resnee ive a. nd ar drawn a p otting boa or: tab e? The, markin eement i. may minim se. ther a.

o a emai and: for; succes of lust ation. willb ons dered to e.- a.pencil...

Data is plotted on the plotting board 4 with the pencil I, the latterbeing suspended by a holder 6 from a so-called transmitting headindicated generally by the reference character 5. The transmitting head5 has been shown in very diagrammatic manner in Fig. 1 inasmuch as thedetails of that device comprise no part of the present invention, sincethat device is the invention of George W. Barnes, Jr., John F. Goetz,and Walter P. Wills and is disclosed in an application, Ser. No. 620,827filed concurrently herewith. A writing handle is preferably attached tothe holdor 6 for the pencil to facilitate the plotting of information tobe transmitted on the plotting board 4. The pencil, when not in use, isautomatically lifted from the plotting board 4 by spring means locatedwithin the holder 6 and disclosed in detail in the Barnes, G-cctz, andWills application. A switch 'I is provided in the pencil holder 5 foractuation by writing pressure of the pencil on the plotting board forthe purpose of actuating a solenoid at the remotely located receivershown in Fig. 2 so that the marking element at the receiver is adaptedto engage the recording chart only when the transmitter pencil is incontact with the plotting board. A knurled nut 8 at the top of thepencil holder is provided to permit the latter to be turned, wherebyplotting can be done from any side of the plotting board. After thepencil holder has been adjusted to a desired posi tion, the knurled nutis tightened.

The transmitting head includes certain of the electrical components ofthe transmitting mechanism and in particular houses variable electricalcondensers 9 and I0, and also includes suitable cams and gimbal jointsso that the condenser 9 is arranged to be varied in capacity inaccordance with the movements of the pencil I along one coordinate, forexample, along the coordinate 2,

while the condenser II] is arranged to be varied in capacity inaccordance with the movements of pencil I in the other coordinate. Thecams referred to serve a compensating purpose required because the angleof the deflection of the pencil holder 6 is not directly proportional tothe 7 linear movement of the pencil I along the plotting board. Thetransmitter head also includes twoelectrical oscillation circuits II andI2, respectively associated with condensers 9 and I0.

Oscillation circuits I I and I2 may be and are shown as being identicalto each other, and therefore, only oscillation circuit II will bedescribed. Components of the oscillation circuit I2 corresponding tothose of the oscillation circuit II have been indicated by the samereference numeral with a prime figure added.

Oscillation circuit II comprises an electron coupled oscillator andincludes a pentode tube I3 which may be of the commercially availabletype 6SJ7. Tube I3 includes an anode, a suppressor grid, 2. screen grid,2. control grid, a cathode and a heater filament. The heater filament isconnected to and receives energy from the secondary winding I4 of acombination stepup-stepdown transformer I5 having a line voltage primarywinding I6 and high voltage secondary windings Il, I8, I9, and 20 inaddition to the secondary winding I4. The terminals of the primarywinding I6 are connected by conductors 2| and 22 to a commercial sourceof alternating current 23, through a double pole-single throw switch 24and a fuse provided to protect the apparatus from damage due toexcessive currents resulting from failure of a component of theapparatus. A lamp 24 connected across the terminals of transformersecondary winding I4 is employed to pro vide a visual indication thatthe switch 24 is closed and the apparatus is powered for operation.

The control grid of tube I3 is connected through a. parallel connectedresistance 25 and condenser 25 to one terminal of a parallel circuit 2?,the other terminal of which is connected to ground G. The parallelcircuit 21 includes in one branch an inductance coil 28 and includescondenser 9 in another branch. The other branches of the parallelcircuit respectively include condensers 29, 30, and 3|. Condenser 3I isshown as adjustable in capacity and is provided for the purpose ofproviding a fine adjustment for the zero setting of the pencil I alongthe coordinate 2. Preferably the condenser 3I is provided with asuitable knob or kerf to facilitate its adjustment. Condenser 29preferably is of the type having a negative temperature coeificient ofcapacitance and is provided to compensate for the effect of ambienttemperature variations upon the frequency of the oscillating currentgenerated by oscillator II.

'The cathode of tube I3 is connected to ground G through an inductancecoil 32 which is disposed in inductive relation to the coil 28 andserves the purpose of feeding back energy from the output circuit of thetube l3 to the circuit of the control grid for maintaining the circuitIi in an oscillat ing state.

As shown, the screen grids of tubes I3 and I3 are connected throughrespective resistors 33 and 31 to the positive terminal 34 of a filterindicated generally by the reference character 35 and having its inputterminals connected to the output terminals of a full wave rectifierdesignated by the character 36. The suppressor grids of tubes I3 and I3are connected directly to ground G.

The oscillating circuit of oscillator II includes 7 the control gridcircuit of which the parallel circuit 21, including the variablecondenser 9, forms a part and also includes a screen grid circuit, whichmay be traced from the positive terminal 34 through resistance 33, thescreen grid of tube I3, the cathode thereof, and inductance coil 32 toground G, which, as shown, constitutes the negative output terminal ofthe filter 35. The screen grid and control grid circuits are inductivelycoupled by the inductance coils 28 and 32 and provide for high frequencyoperation through a range varying from approximately 390 to 470kilocycles, depending upon the position along the coordinate 2 of thepencil I. Similarly, the inductance coils 28 and 32' of oscillationcircuit I2 provide for high frequency operation through a frequencyrange varying from approximately 390 to 470 kilocycles, depending uponthe position of the transmitter pencil I along the coordinate 3.Accordingly, the oscillation circuits II and I2 each produce a highfrequency oscillating current having a frequency Within the range of 390to 470 kilocycles, depending upon the position to which the pencil I ofthe transmitter is moved relatively to the coordinates 2 and 3.

Energizing current is supplied the anode circuits of the oscillationcircuits I I and I2 from the rectifier 36 and filter 35 through acircuit which may be traced from the output terminal 34 of filter 35through a conductor 42 to the junction of a pair of resistors 43 and 44.The other terminal of resistor 43 is connected to the anode of tube I3of oscillation circuit II, while the other terminal of resistor 44 isconnected to the anode of tube I3 of oscillation circuit I2. Thecathodes of tubes I3 and I3 are connected through their respectivelyassociated feedback coils 32 and 32 to ground G and-thereby to thenegative output of fllter- 38. It is noted that ground G is connected bya resistor 45 to the junction of the transformer secondary windings I8and I9 whereby the potential of the junction point of windings l8 and I9is maintained a suitably negative with respect to ground potential.

In order that both of the high frequency oscillating signals generatedby the oscillation circuits II and I2 may be amplified by a commonamplifier and both amplified quantities may be conducted over the sametransmission lines to the remotely located receiving station, theoscillating currents produced by the oscillation circuits II and I2 arealternately interrupted at suitable frequency, and in particular, at thefrequency of the voltage supplied by source 23. To this end there areprovided keying and amplifying tubes 38 and 39. Tubes 38 and 39 alsoserve as bufl'er tubes to increase the stability of the respectively.assoscreen grid of tube 38 for amplifying and transmission purposes,while the output circuit of oscillation circuit I2 is coupled by meansof a condenser 4I to the screen grid of tube 39 for the same purposes.

Energizing current is supplied the anode circuits of the tubes 38 and 39from the rectifier 36 and filter 35 through a circuit which may betraced from the positive output terminal 34 of the filter to thejunction of resistors 33 and 31. The other terminal of resistor 31 isconnected to the anode of tube 38,v while the other terminal of resistor33 is connected to the anode of tube 39. The cathodes of tubes 38 and39. are connected together and to the junction of transformer secondarywindings I8 and I9. Since the potential of the last mentioned junctionpoint is negative with respect to ground by an amount determined by themagnitude of resistor 45 and the magnitude of current flowing throughit, the anode voltage impressed on the tubes 38 and 39 is ofcorrespondingly greater magnitude than that impressed on the anodecircuits of tubes I3 and I3. Resistor 45, accordingly, is so chosen asto provide the proper operating anode voltages for tubes 38 and 39.

The suppressor grids of tubes 38 and 39, as shown. are directlyconnected to the cathodes of said. tubes. 1

Energizing voltage is supplied the screen grids of tubes 33 and 39 fromthe rectifier 36 and filter 3.5 through a circuit which may be tracedfrom the filter output terminal 34' to the junction point of resistors45' and 46. The other terminals of resistors 45' and 46 are connected torespective screen grids of tubes 38 and 39.

Separate alternating voltages 180" out of phase with each other areimpressed on the control grids of tubes 38 and 39 from the transformersecondary windings I9 and I8, respectively. Specifically, the cathodesof tubes 38 and 39, as previously noted, are connected together and tothe junction point. of windings. I8 and I9. The other terminal ofwinding I9 is connected through a resistor 41 to the control grid oftube 38, while. the other terminal of winding 18 isconnected througlraresistor19to the control grid of tube 39. The alternating voltages thusimpressed on the control grids of tubes 38 and 39 are of the propermagnitude to render the tubes 38 and 39 non-conductive during alternatehalf cycles of the alternating voltage supplied from the alternatingcurrent source 23.

In order to periodically interrupt the oscillating signals generated bythe oscillation circuits II and I2. at the frequency of the alternatingvoltage supplied from source 23, the screen grid of tube I3 is connectedto the junction of resistor 33 and the anode of tube 39 and the screengrid of tube [2 is connected to the junction of resistor 31 and theanode of tube 38. When tubes 38 and 39 are rendered conductive, thepotential of their respectively associated anodes decreases with respectto ground potential. The reduced anode voltages are sufficiently lowwhen applied to the screen grids of tubes I3 and I3 to cause the lattertubes to be rendered non-conductive. Hence, tube I3 is arranged to berendered nonconductive during the half cycle that tube 39 is conductive.During that half cycle tube 38 is non-conductive, and in consequence,tube I3 will be conductive and an oscillating signal will be produced byoscillation circuit I2. In the next half cycle tube 38 will beconductive and the oscillating signal produced by the oscillationcircuit I2 will be interrupted. During this latter half cycle the tube39 will be non-conductive, and as a result the oscillation circuit l Iwill be operative to produce an oscillating signal. The fluctuatingvoltages so created and impressed on the screen grids of oscillatortubes I3 and I3 change rapidly from a value at which the oscillators arepermitted to oscillate to a value at which oscillation is interrupted,and consequently, the interruption and initiation of the state ofoscillation of tubes ['3 and I3 is clean and sharp.

Specifically, assume that the voltage applied to the control grid oftube 38 is traversing its positive half cycle while the voltage appliedto the control grid of tube 39 is traversing its negative half. cycle.The amplitude of the voltage applied to the control grid of tube 39 issufficient to quickly block or cut ofi conduction through tube 39.Therefore, this tube is efiectively eliminated from the circuit and thescreen grid of oscillator tube I3 receives its full operating voltagefrom the output terminal 34 of the filter 35. It. is important to notethat during operation of the oscillation circuit II the operatingvoltages applied to the electrodes of tube I3 are constant for allpractical purposes and consequently no frequency modulations occur dueto periodically varying values of operating voltages.

During the half cycle under consideration tube 3.8 is conducting and thesteady D. 0. component of its anode current effects a sharp decrease inthe voltage of its anode, which voltage is also the voltage applied tothe screen grid of oscillator tube I3, to such a value that conductionthrough the oscillator tube I3 is suddenly cut off. It is noted that cutofi of tube I3 is readily accomplished because the. anode voltage oftube 38 may become zero or even go slightly negative. with respect tothe potential of the cathode of tube I3 and still provide an operatingvoltage for the anode of tube 38 of amount sui'ficient to maintainconduction through tube 38. This operation is made possible because ofthe negative voltage applied to the tube 38 cathode by virtue of thelatters connection to the junction of transformer secondary windings I8and I9,

which, as previously indicated, is negative with respect to groundpotential.

In the half cycle under consideration the tube 38 is utilized as abuffer for the oscillation circuit l2 and also serves to amplify theoscillations produced by that oscillation circuit. To this end, theanode of tube I3 is connected by condenser 49 to the screen grid of tube38. It is noted that the circuit constants are not critical as long asthe most positive voltage which the anode of tube 38 may assume duringthis interval determined by the direct current and radio frequencyvoltage drop across the anode resistor 31 is sufficient to preventoscillation of the oscillation circuit l2. For the next half cycle ofthe voltage supplied by source 23, the reverse of the above conditionsexists. That is to say, tubes 38 and I3 are cut off while tubes 39 andI3 are rendered conductive. Hence, during this half cycle theoscillation circuit [2 produces an oscillating signal and thisoscillating signal is amplified by tube 39 which also serves a bufferpurpose. To this end, the anode of tube I3 is connected throughcondenser to the screen grid of tube 39.

As those skilled in the art will recognized, it is possible to utilizein place of the tubes 38 and 39, tubes such as the commerciallyavailable type 6L7, or any other frequency mixer or pentagrid convertertube conventionally used in heterodyne radio broadcast receivers. Suchtubes are provided with two control grids, and therefore the oscillatingsignals from the oscillation circuits H or I2 to be amplified may beapplied to one control grid while the keying voltage derived from thetransformer secondary windings l8 and I9 is applied to the other controlgrid. The use of such tubes in place of the tubes 38 and 39 isadvantageous in that the oscillating signals to be amplified are alsoapplied to a control grid, and therefore, will be amplified to a higherdegree than they are when applied to a screen grid as shown in Fig. 1.

In Fig. 3 we have illustrated another modification of the arrangement ofFig. l for alternately interrupting the oscillating signals produced bythe oscillation circuits II and I2 and for amplifying those oscillatingsignals. The circuit arrangement of Fig. 3 is substantially identical tothat of Fig. 1 with the exception that the keying voltages from thetransformer secondary windings l8 and I9 are impressed on the screengrids of tubes 38 and 39 and the oscillating signals to be amplified areimpressed on the control grids of those tubes. Specifically, the voltageof the transformer secondary winding 18 is impressed on the screen gridof tube 39 through a circuit which may be traced from the said controlgrid through the winding l8 and through a biasing resistor 50 to thecathode of tube 39. Similarly, the voltage of winding I9 is impressed onthe screen grid of tube 38 through a circuit which may be traced fromthe said screen grid through winding [9 and through a biasing resistorto the cathode of tube 38.

The oscillating signals produced by oscillator II are impressed on thecontrol grid of tube 38 through condenser 4 0, while the oscillationsignals produced by oscillator l2 are impressed through condenser 4| onthe control grid of tube 39. As shown, the control grids of tubes 38 and39 are connected by individually associated resistors 52 and 53 to thenegative terminals of biasing resistors 59 and 5|, which terminals areconnected together and to the junction of transformer secondary windingsl8 and I9.

The manner of operation of this modification of our invention isotherwise the same as that shown in Fig. 1, and hence, furtherdescription thereof is believed unnecessary. Here again circuitconstants are not critical, as long as the most positive voltage whichthe anodes of tubes 38 and 39 may assume during the alternate halfcycles that they are conductive is sufficiently low to prevent operationof the respectively associated oscillation circuits 1! and II.

From the foregoing description it is evident that in each contemplatedembodiment of my invention, the interruption of the oscillating signalsproduced by the oscillation circuits H and I2 are timed so that oneoscillation circuit ll generates an oscillating signal only when theoscillation circuit I2 is cut off and vice versa. Moreover, theinterruption of the oscillating signals from the oscillation circuits Il and 12 occurs at the frequency of the alternating voltage suppliedfrom the source 23. In other words, during one half cycle of thealternating voltage supplied by source 23, the oscillation circuit II isoperative to generate an oscillating signal and that oscillation signalis amplified by the tube 38. During the next alternate half cycle theoscillation circuit I2 is operative to generate an oscillating signaland that signal is amplified by the tube 39. Therefore, the tubes 38 or39 which generate a voltage for interrupting one of the oscillatingsignals are also used to amplify the output of the other oscillationcircuit during the cut off period of the first oscillation circuit. Thesecond tube 38 or 39 which generates a voltage for interrupting theother oscillation circuit performs a similar amplifying function for thefirst oscillating circuit. This amplification stage comprising tubes 38and 39, as previously noted, also serves to increase the stability ofthe oscillation of oscillation circuits II and I2 by reducingfluctuations in the oscillation circuit loads.

In order to further amplify the oscillating signals generated by theoscillation circuits II and I2 sufficiently for transmission of thoseoscillating signals to the remotely located receiving station orstations, there is provided an additional amplifier indicated generallyby the reference character 54. This amplifier 54 also performs theadditional function of matching the impedance of the output circuit ofthe transmitter to that of the receiving circuit to obtain maximum powertransference.

As shown, the transmitter amplifier 54 includes a tube 55 which maydesirably be of the commercially available type 6A0? and includes anode,suppressor grid, screen grid, control grid, cathode, and heater filamentelements. Anode voltage is supplied tube 55 from the rectifier 3G andfilter 35 through a circuit which may be traced from the positive outputterminal 34 of the filter through a resistor 56 to the anode of the tube55, the cathode thereof, and through a biasing resistor 51, shunted by acondenser 58, to ground G and thereby to the negative output terminal ofthe filter.

Energizing voltage is supplied to the screen grid of tube 55 through acircuit which may be traced from the positive output terminal 34 of thefilter through a resistor 59 to the screen grid. the cathode and theparallel connected resistor 51 and condenser 58 to the negative andgrounded output terminal of the filter. The screen grid is alsoconnected by a condenser 60 to ground.

respective condensers BI and 62 to the control grid of tube 55 which, asshown, is also connected by resistor 62' to ground G, and the cathodesof tubes 38 and 39 are connected through resistor 45 to ground G andthrough the parallel connected resistor 51 and condenser 58 to thecathode of tube 55. Tube 55, therefore, operates to amplify theoscillating signals in the output circuits of both tubes 38 and 39. Theamplified quantity derived from tube 55 is resistance coupled by meansof a condenser 63 and a resistor 64 to the input circuit of a tube 65which is provided for the purpose of matching the impedance of theoutput circuit of transmitter amplifier 54 to the characteristicimpedance of a transmission line connecting the transmitter to theremotely located receiver.

Tube 65 may be of the commercially available type 6V6 and includes ananode, a screen grid, a control grid, a cathode, a heater filament, andalso a pair of beam forming plates. Energizing voltage is supplied tothe anode circuit from the rectifier 36 and filter 35 through a circuitwhich may be traced from the positive output terminal 34 to the anode oftube 65, the cathode thereof, and through an output resistor 66 to thenegative and grounded terminal of the filter. Energizing voltage issupplied the screen grid of tube 65 through the same circuit. The beamforming plates, as shown, are directly connected to the cathode. Thecontrol grid of tube 65, as shown, is directly connected to the junctionof condenser 63 and resistor 64 and thereby is coupled to the outputcircuit of tube 55.

While the rectifier 35, filter 35, and transmitter amplifier 54 havebeen shown in Fig. 1 as being located closely adjacent the plottingboard 4, it will be understood that, if desired, these components may belocated at a distance with respect to the plotting board and also withrespect to the oscillation circuits II and I2. For example, in someapplications it may be desired to locate the plotting board 4 and theoscillation circuits II and I2 in one room and to have the rectifier 36,filter 35, and the transmitter amplifier 54 in another room to the endthat the transmitting mechanism visible for manipulation by an opera--tor may be made less cumbersome and bulky.

This feature is also advantageous when the transmission system of thepresent invention is utilized on shipboard in which the space availableis at a premium and would preclude the cation of all of the transmittingequipment closely adjacent the plotting board 4 and overhead transmitterunit 5. In a practical operating embodiment of the present invention, ashielded cable 25 feet long is provided between the plotting board andthe circuit components including the rectifier 36, filter 35, andamplifier 54.

Tube 65 is connected to operate as a cathode follower, that is to say,the output signal which is transmitted to the receiver is derived fromthe resistor 65 connected in the cathode circuit of the tube. Resistor66 is so chosen as to have characteristic impedance approximating thatof the transmission line L connecting the transmitter to the receiver.As shown, the terminal of resistor 66, which is connected to thecathode'10 of tube 65, is coupled by a condenser 61 to one terminal of thetransmission line L, while the other and grounded terminal of theresistor 66 is connected directly to another terminal of thetransmission line.

At the transmitter amplifier 54 there is also provided a relay 68, oneterminal of the operating coil of which is connected to the ungroundedside of transformer secondary winding I4 and the other terminal of whichis arranged to be connected to the grounded side of winding I4 uponclosure of the switch I attached to the writing pencil or stylus I. Tothis end, one terminal of the switch I, as shown, is connected directlyto ground G. When the switch 1 is closed, as upon movement of the pencilI into engagement with the plotting board 4, the relay 68 is energizedand closes an associated switch 69 to energize a solenoid 10 attached tothe recording pen mechanism in the receiving unit to move the pen intoengagement with the recording chart. When the switch 1 is open and therelay 68 is deenergized, the switch 69 is also open, and the pen at thereceiving unitis moved out of engagement with the recording chart by theaction of gravity, the solenoid 10 then being deenergized.

As has been previously mentioned, the apparatus located at the remotestation, where the transmitted writing or other data is to bereproduced, is arranged to translate the adjustable frequencies of theoscillating signals generated by the oscillation circuits II and I2 intotwo coordinates of pen position. More specifically, the receivingapparatus operates to move the recording pen in a vertical direction inaccord ance with the variations in frequency of the oscillation signalgenerated by the oscillation circuit II, and operates to move therecording pen in a horizontal direction in accordance with the frequencyvariations of the oscillation signal generated by the oscillationcircuit I 2. In this manner the changes in position of the pencil orstylus along the plotting board 4 at the transmitter may beexactlyreproduced at the receiving apparatus.

By reference to Fig. 2, it will be noted that two independent receivingcircuits are provided. One of the receiving circuits controls themovement of the recording pen in one coordinate, for example, thehorizontal coordinate, and the other receiving circuit controls therecording pen in the vertical coordinate. The oscillating signalsderived from each of the oscillation circuits I I and. I2 andtransmitted to the receiver over the transmission line L are impressedon both of the input circuits of the two receiving circuits. Thereceiver mechanism is so arranged that one of the receiving circuits isresponsive only to the oscillating signal generated by the oscillationcircuit H, and the second receiving circuit is responsive only to theoscillating signal generated by the other oscillation circuit I2 tocontrol the energization of individually associated reversible motors,which in turn are linked by suitable mechanical means to the recordingpen to position the latter in the two coordinates along the recordingchart. The operation of the two receiving circuits is the same, and thefollowing explanation applies to both circuits. One of the receivingcircuits has been generally indicated by the reference character II andthe other by the reference character H. The elements of "the receivingcircuit 1 I corresponding to those of the receiving circuit II have beenindicated byv 11 the same reference numerals with a prime figure added.

The receiver ll includes two stages of amplification. the first of whichutilizes an amplifying tube 12 of the commercially available type SAC?and. the second of which utilizes an amplifying tube 13 of the type 6V6.In the second stage of amplification the two oscillating signals fromthe transmitter are separated and one of them is rejected. In otherwords the second stage of amplification responds only to the oscillatingsignal generated by one of the oscillation circuits l I or I2 and, forpurposes of illustration, will be assumed to respond only to theoscillating signal generated by the oscillation circuit l I. Rejectionof the oscillating signal from the oscillation circuit I2 isaccomplished in a manner described in detail hereinafter, and generallyspeaking, involves the application of an alternating voltage derivedfrom source 23 to periodically interrupt the conduction of tube 13. Theoscillating signal after rejection of the undesired portion consists ofa radio frequency wave which is periodically interrupted at thefrequency of the voltage supplied by the source 23 and has beenillustrated schematically in graphs (b) and (bb) of Fig. 4 which showthe oscillating signal frequency as being higher and lower,respectively, than a frequency value at which the receiving pan is heldmotionless along the vertical coordinate.

Tube 12, as shown, includes anode, suppressor grid, screen grid, controlgrid, cathode, and heater filament elements. Energizing current issupplied the heater filament from the low voltage secondary winding 14of a transformer 15 having a line voltage primary winding 16 which isconnected by conductors l8 and 19 to the alternating voltage source 23.To this end the conductors I8 and 19 are included in the shielded cableL connecting the trammitter to the receiver. The transformer 15 alsoincludes high voltage secondary windings 80 and 8 l both of which areprovided with a center tap.

Energizing voltage is supplied to the anode of tube 12 from a full waverectifier indicated. generally by the reference numeral 82 and a filterindicated at B3. The rectifier 82. energized by the transformersecondary winding 80, provides a voltage at the output terminal 84 ofthe filter 83 which is suitably positive with respect to the potentialof ground G to which the negative terminal of the filter is connected.As shown. the positive terminal 84 is connected through a resistor 85 tothe anode of tube 12, and the cathode is connected through a parallelconnected resistor 85 and condenser 81 to ground G. Energizing voltageis supplied to the screen grid of tube .12 from the positive filteroutput terminal 84 through a circuit, including a resistor 88, to thescreen grid and from the cathode through the parallel connected elements86 and 81 to ground G.

As may be seen by reference to Figs. 1 and the output terminal ofresistor 66 of the transmitter amplifier 54, which is connected to thecathode of tube 65, is connected by condenser 61 and the shieldedtransmission line L to the control grid of tube 12. The other andgrounded output terminal of the transmitter amplifier 54 is connectedthrough the transmission line L to the parallel connected resistor 86and condenser 31 and thereby to the cathode of tube 12.

The output circuit of tube 12 is coupled by a condenser 89 and aresistor 90 to the input circuit of tube 13. Tube 13 includes an anode,a screen grid, a control grid, a cathode, a heater filament,

and beam forming plates. Energizing current is supplied to the heaterfilament from the low voltage transformer secondary winding '14.

Anode voltage is supplied to tube 13 through a circuit path which may betraced from the positive output terminal 84 of the filter 83 through aparallel network including in one branch the primary winding 95 of atransformer 98 to the anode of tube 73, the cathode thereof, and aparallel connected resistor 92 and condenser 93 to the grounded andnegative terminal of the filter. The other branches of the parallelnetwork respectively include a resistor 9i and a condenser 94. Thetransformer 98 comprises a part of a frequency discriminator indicatedgenerally by the reference numeral 91 and includes a split secondarywinding in addition to the primary winding 95.

The beam forming plates of tube 13 are directly connected to thecathode, and. the control grid is coupled to the output circuit of tube'12 by virtue of its connection to the junction of condenser 89 andresistor 90.

Alternating voltage is impressed on the screen grid of tube 13, forperiodically rendering it nonconductive, from one half of the centertapped transformer secondary winding through a circuit which may betraced from lower terminal of the winding 80, seen in the drawing,through a resistor 98 to the screen grid of tube 13 and through theparallel connected elements 92 and 93 to ground and thereby to thecenter tap on winding 80. The screen grid of tube 13 is also connecteddirectly to ground G by a condenser 99. The magnitude of the alternatingvoltage impressed on the screen grid of tube 13 is so chosen as to besufiicient to cause the tube 13 to be rendered non-conductive or cut oilduring those hall cycles of the voltage of source 23 in which the screengrid is driven in the negative direction. Furthermore, the phase of thisalternating voltage is such that the tube 13 is operative to amplify theoscillating signals generated by the oscillation circuit I I andtransmitted to the receiver "H only during those alternate half cyclesof the supply line voltage in which the oscillation circuit II isoperative to generate an oscillating signal.

It is noted that the entire transmis receives energizing current fromthe sin 23 of alternating current. This source. de' scribed, is locatedat the transmitter amplifier unit and the alternating current utilizedfor. energizing the receiving units is transmitted from the source 23 byway of the transmitting cable L. This is done to insure synchronism ofthe keying action of the transmitter and receiver units and alsoprovides the advantage of permitting the installation and use ofreceivers at locations where there is not available alternating power ofthe same frequency and phase as that delivered by source 23.

The frequency discriminator 97, previously referred to, includes inaddition to the transformer 96 pair of diode rectiflers Hi9 and Iili,which desirably may be contained within a sin le envelope. generallydesignated at Hi2. One half of the split secondary winding of theintermediatev frequency transformer 96 has been designated 0*! thenumeral I03 and the other half by the nu- Ineral I04. The center tap ofthe split secondary winding comprising the junction of winding sectionsI03 and I04 is connected through a blocking condenser I05 to the anodecircuit of tube 13, and more specifically, to the terminal of theprimary winding which is connected to the anode gun-no.

13 of the tube 10.. The center tan of the split secondary winding isalso connected to the point of engagement of apair'of resistors ["86and-N1. The,

resistors I06 and I01 are shunted by a resistor I08 which isprovidedwith an adiustable tap I09. The usable output voltage from thefrequency discriminator is obtained. across the resistor 1.08 which, asshown, is shunted by a condenser H0.

The diode rectifiers I00 and MI may be'contained within a single tubesuch as the commercial-ly available type. 6H6. Each diode includesanode, cathode, and heater filament elements. The heater filamentelements are connected in series with each other and receive energizingcurrent from the transformer secondary winding I4. The cathodes ofthe'diodes I00 and I0=I are connected through resistors I06 and Ill-I,respectively, to the junction of' the transformer secondary windings I03and I04. The other terminal of the winding. I03 is connected to theanode of diode I 00, while the other terminal of the winding I04 isconnected to the anode of the diode I'M.

For tuning the secondary winding of the transformer 96 to the frequencyof the oscillating signals impressed thereon from the output circuit oftube I3, a variable condenser II I is provided. This variable condenseris arranged to be automatically adjusted in capacity as required tomaintain the secondary winding of the intermediate frequency transformer96 tuned to the frequency of the applied oscillating signals. A variablecondenser I I2 and a variable inductance H3 are connected in shunt withthe secondary winding of thetransformer 96 for a purpose which will belater explained.

The blocking condenser I05 and the condenser H0 are so selected as topresent lowimpedance to the radio frequency oscillating currents flowingthrough them. The condenser 94 and the transformer primary Winding 95connected in parallel therewith are so' selected as to provide highimpedance in order to produce a large'output signal from thediscriminator. Preferably the primary winding 95 is tuned to a valuewhich is outside the range of frequency variation of the oscillatingsignals generated by the oscillation circuit II' at the transmitter andimpressedon the receiver circuits. By way of example it is noted thatsatisfactory operation has been obtained' when the primary winding 95 istuned to a frequency of'325 kilocycles. The tuning of the primarywinding 95 to this value which is below the operating range of frequencyvariation of the oscillating signals conveyed by the transmission line Lto the receiver H consti utes no part of the present invention but isthe sole invention of the joint applicant Rudolf 1". Wild and is beingdis closed and claimed in. application, Ser. No. 620,831, filedconcurrently herewith.

The frequency discriminator 9'! together with the diodes I00 and IN is,provided for the purpose of deriving a voltage having an alternatingcomponent of one phase or of opposite phase and of the same frequency asthe voltage supplied by source 23 accordingly as thefrequency oftheoscillating signal impressed thereon from the output circuit of tubeI3 is higher or'lower than the frequency value to which the splitsecondary winding of transformer 96 is tuned. The details of thisfrequency discriminator constitute no part of the: present invention.Its manner of operation and arrangement are disclosed in theaforementioned application of R. F; Wild and'also in the copendingapplication, Ser. No. 537,505, filed 14 May 26,1944, of R. F. Wild, andtherefore, need be only briefly described herein.

Itv is believed sufficient to note that if the fre quency of the appliedoscillating signal is the 3 value towhich the secondary winding of theintermediate frequency transformer 96 tuned, the outputs of the dioderectifiers I00 and IM cancel each other and zero voltage appears acrossthe output resistor I08 of the frequency discriminator circuit 91. Ifthe frequency of the applied oscil-' lating signal is a value other thanthat to which the secondary winding of the transformer 96 is tuned, thephase relations of the voltages applied to. the diode rectifiers I00 andNH are such that their outputs do not cancel and a direct currentvoltage appears across the output resistor I08. The polarity of thisvoltage depends upon whether the frequencyof the applied oscillatingsignal is above or below the value to which the secondary windingof thediscriminator is tuned. The magsince the applied oscillating signal isperiodically interrupted at the frequency of the alternating voltagesupplied by source 23, the pulsations of direct current voltage producedacross resistor I08 have the same frequency as the voltage supplied bysource. Graphs (c) and (cc) of Fig. 4 illustrate the voltage outputproduced across the resistor I08 for the respective cases of high andlow frequency of the applied oscillating signal.

The pulsating voltage produced across the resistor I08 may be consideredas comprising two components. (1) a steady D. C. component and (2) an A.C. component. The A. C. component obtained when the frequency of theapplied 05- cillating signal is higher than the value to which thesecondary winding of the frequency discriminator is tuned is shown ingraph (d) of Fig. 4 while graph (dd) of Fig. 4 illustrates the A. C.component obtained when the frequency of the applied oscillating signalis lower than the value to which the secondary winding of the frequencydiscriminator is tuned.

The variable condenser H2 connected in parallel with the discriminatorsecondary winding is a trimmer condenser and serves to provide for zeroadjustments of the recording pen along the vertical coordinate. To thisend the condenser H2 is provided with a suitable knob or kerf forfacilitating its adjustment.

In order to provide for span adjustment or,

in other words, the extent of variation of condenser Ill required totraverse the entire fre-' quency' range of operation, the variableinductance H3 is provided. Inductance H3 is preferably provided with anadjustable iron core. A suitable knob or kerf is preferably provided onthe inductance H3 to facilitate its adjustment.

The zero and span adjustments described comprise no part of'the presentinvention, but aredisclosed and claimed in the application of R. F. Wildbearing Serial No. 620,832, filed concurrently herewith.

The alternating component of the pulsating voltage produced acrossresistance I08 is amplifled by a stage of voltage amplificationincluding a tube H4, which stage of amplification incorporates a gaincontrol for manually adjusting the sensitivity of the receiving unit.This gain control comprises the provision of slider contact I09 inassociation with the resistor I08 for tapping off and impressing on theinput circuit of tube H4 a variable portion of the voltage producedacross the resistor I08. Tube II4 may be of the commercially availabletype 6AC7 and includes anode, suppressor grid. screen grid, controlgrid, cathode, and heater filament elements. Energizing current issupplied the heater filament from the transformer secondary winding '14.Anode voltage is supplied tube H4 from the rectifier 82 and the filter83 and to this end the positive terminal 84 of the filter 83 isconnected through a resistor I I5 to the anode of tube I I4, and thecathode of the latter is connected through a resistor II6 to thegrounded and negative terminal of the filter. Energizing voltage issupplied the screen grid through a circuit which may be traced from thepositive terminal 84 through a, resistor H! to the screen grid, thecathode, and resistor H6 to the grounded and negative terminal of thefilter. A condenser I I6 is connected between the screen grid of tube II4 and ground, as shown.

The output circuit of tube H4 is coupled by a condenser H9 and aresistor I20 to the input circuit of a motor drive stage indicatedgenerally by the reference character IZI. Motor drive stage I2I is shownas including triodes designated by the numerals I22 and I23,respectively, but it is preferred to utilize a number of such triodesconnected in parallel with each other instead of single triodes. Forexample, in. a practical operating embodiment of the invention, threesuch triodes I22 and I23 were connected in parallel, thus insuring thederivation from the motor controlled by the tubes of suflicient torqueto actuate the recording pen.

As shown, the tubes I22 and I23 each include anode, control grid,cathode, and heater filament elements. Energizing voltage is suppliedthe heater filament elements in series from the transformer secondarywinding 14. Anode voltage is supplied tubes I22 and I23 from thetransformer secondary winding BI and to this end one end terminal ofwinding BI is connected to the anode of tube I22 and the other endterminal of that winding is connected to the anode of tube I23. Thecathodes of tubes I22 and I23 are connected together and through abiasing resistor I24 to one terminal of the control winding I25 of areversible two-phase induction motor I26. In addition to the WindingI25, the motor I26 includes a second winding I21. A condenser I28 isconnected in parallel with winding I25 and the other terminal of thelatter is connected to the center tap of the transformer secondarywinding 8|. Accordingly, energizing current is delivered to the motorwinding I25 from the transformer secondary winding BI under control ofthe triodes I22 and I23. Winding I2I of the motor I26 is connectedthrough a condenser I29 and conductors I8 and I9 to the source ofalternating current 23.

Thus, the output current of the tubes I22 and I23 is utilized to deliverener y to winding I25 of the motor I26, and the power winding I21 ofthat motor is connected to the alternating current power supply throughcondenser I29. The motor is actuated for rotation when an alternatingcurrent signal of the frequency of the volt age supplied by source 23 isimpressed on the input circuits of tubes I22 and I23. For accomplishingthis result the control grids of triodes I22 and I23 are conectedtogether and to the junction of condenser H9 and resistor I20.

Referring to graphs (d) and (dd) of Fig. i, it will be seen that the A.C. component oi the dis criminator output voltage reverses in phase whenthe frequency of the applied oscillating signal changes from below toabove that to which frequency discriminator is tuned. This chap phasewhen applied to the control grids of tri I22 and I23 causes a decreasein the conduc-tiv y of one triode I22 or I23 and a corresponding increase in the conductivity of the other triode. In consequence,energizing current is delivered to the control winding I25 of the motorI26 which leads or lags by approximately the voltage of source 23depending upon which triode I22 or I23 has had its conduction increased.Stated differently, this change in phase of the volt {e derived from thefrequency discriminator cai: reversal of the direction of rotation oi"the reversible motor I26.

The details of this motor drive circuit comprise no part of the presentinvention, since that circuit is the invention of Walter P. Wills and isdisclosed in a copending application, Ser. No. 421,173, filed December1, 1941, now Patent No. 2,423,540 of July 8, 1947, and hence, requiresno further description herein.

The shaft of motor I26 is geared in any suitable manner, not shown inorder to avoid complication of the drawing, to the variable condenselIII connected in the frequency discriminator. The shaft of motor I26 isalso mechanically coupled to the recording pen of the receiver andadjusts both the condenser I II and the recordin pen until the secondarywinding of the frequency discriminator is tuned to the frequency of theapplied oscillating signal. Inasmuch as the output of the frequencydiscriminator is zero Wi'iG'l'l it is tuned to the frequency of theapplied 05.... lating signal, the motor then stops and is main-- tainedstationary until the frequency of the applied oscillating signal againchanges.

In Fig. 2 a portion of the receiving instrument containing the recordingchart is broken away to show a pen carriage I30 which has a pen I3Imounted thereon. The carriage I311 is actuated for movement in verticaland horizontal direc tions by bars I32 and I33, respectively. Thesupporting bars for the carriage have rollers I36 and I35, respectively,on their ends, which ride on individually associated tracks I36 and I3I,which are provided in the base of the receiving instrument. As the rodsI32 and I33 are moved, the pen carriage I3I will be moved in anydirection underneath the chart indicated generally by the referencenumeral I38. If rod I32 only is moved as upon operation of motor I26,the carriage i3I will be moved in a vertical direction only. Similarly,if rod I33 only is moved, as upon operation of motor I26, the carriageI3I will be moved in a horizontal direction only. If rods I32 and I33are simultaneously moved, the pen carriage I3I will be moved at an angleto both sides of the instrument. Movement is imparted to the rod I32, aspreviously stated, by the motor I25, which has a drive pulley I39attached to it. This pulley drives a cable I40 that passes over suitableguide pulleys at opposite ends of the track I 38 and which is fastenedto the roller I34. In a like manner motor I26'.is utilized to impartmovement to the rod I33, and to this end motor I 26 has a drive pulleyI4I fastened to its shaft. As the pulley armies I4 I rotated-it drives'a-"cable l 4-2 anew aroun'd suitabl guiddpulleys the ends smack m andwh-ili is attacnemetnemner m- Iii-consequence; as the mctors -1 2sand-I26 energized forrot'altibrid-ri one' directietr 'or -the other 11 1responsew dihei rceptioii -of oscillatin signals fromthe trarisiiiittthe en? t3 t avili' be' adi'u's'te d' relativel-y to -the chart -438 'toproduc an -exaot 'reproduc'tion crthe' i'novement iniparted to thewriting stylusor"pencil at the-transmitter relatively toth' plottingboardl As -previousl I noted; u on' movemen :cr tne writingi'astyius orpencil unto eng'ag'ement with ime plotting board energization of thesolenoid for littlri'g' ithe' -m recording ups into engagenie'ntvt'itl'i th re cordingfchart I 38; :In" consequence th' re'cording pen l3 t is operativeto'ttac'e tnepatn of 'its move ment' on the chart I38'o'ni'y' when the wr i ting' pen in oil or stylus at the transmitter isin contact with m the? plotting boards: z

This arrangement in which the 'recordingsmeoh ll anism is locatedentirely beneath the chart and: thereforarleaVes the can or the 'cha'rtiree for: in-

closed in this appiication'iandarelat-ingto' an elec i Serial Number12,873, filed March 3, 1948$ Whileiin' accordanceiwith the provisions ofthe statutespwe 'ihaiie illustrated and described the best forms of theinvention now known to us, it will be apparent 'to -those skilled in theart that changes may be madecinitheeform-of-ithe. appa-- ratus disclosedwithout departinglfrom the spirit in of the invention as set forthin'theappended claims, and that in-some==caseseertain' features of theinventi n may sometimes-bowsed to advan zz' tagewithout-a correspondingusewof other ifea sl turesi Having nowdescribed our invention, what wveclairn as newand desire to secure by Letters? Patent, is; a

1. In an electrical transmission' s'ystem;'i'first and secondoscillation generators for producing 15 separate electrical signals tobe transmitted, each oscillation generator having an output circuit andan input circuit for adjusting the oscillation generator to itsoscillating and non-oscillating condition, a common transmission circuitfor both 5' of said signals, first and second electron discharge deviceseach having an input circuit and an output circuit, means to alternatelyrender each of said electron discharge devices inoperative, meansconnecting the output circuits of both of said no electron dischargedevices to said transmission circuit, means connecting each of theoutput circuits of said first and second oscillation generators to arespectively associated input circuit of said electron dischargedevices, and means connecting each of the input circuits of said firstand second oscillation generators to a respectively associated outputcircuit of said electron discharge devices whereby said firstoscillation generator is operative and the signal produced thereby isrelayed by one of said electron discharge devices to said transmissioncircuit only when the other of said electron discharge devices isinoperative, and said second oscillation generator is operative and thesignal produced 7 thereb y is relayed-by said -other-electron dischargddev'ice to said transmission circuitonly when said one electrondischarge device is inoperative.**

2. In an electrical transmission -system, first and second oscillationgenerators" forproducing separate electricalsignals to be t-ransmitted;each oscillation generator havingamoutputcircuit'and' an input circuitfor adjus'tingthe" oscillation genorator-to its 1 oscillating and "nonoscillatfing' conditi om -"a commontransmission"circuitfor both i ofsaid signals; first "and-second electron dis charge iievices each havingandnputcircuit andan output circ'uit; means to alternately *rendereach-of said electron discharge devicesinoperm five-means connectingthe'output circuits of both of an electronfdischarge devics to-said-=transmission-circuit} means connecting eacirof the"outputcircuits of said first and second oscilla tion generators totheinput circuits of said first f and second electron discharge -device's,respec tiv'elyyandmeans connecting each of theinput circuitsof-s'aid"first andsecond o'sciilation generators to the output circuits of said"second and first electron dischargedevices; *respectively, whereby saidfirst -oscillit't'ion'generater-is 'ope'rative and the signal produced"ther'ebyis relayed by said first electron'di'scharge"deviceto saidtransmission circuit-only When=saidsecond electron 1 discharge device isinoperative, and said second o'scillatioii"generatof is operative *andthe signal producedthereby' is' -relayed by'said" second electron"discharge device'ftdsaid transmission circuito'nlywhens'aidflrst'electrondischarge de--' lis vic'e is inoperative- 3. Inan" electrical transmission-system, "first and 'second="dscillationgenerators "for producing 1: separate electrical signals to betransmitted; each oscillationgenerator' having'an output circuit and aninput circuit "for adjusting the oscillation L 1' generator to as*oscillating""and" non-oscillating condition?" a "common" transmission 1-circuit for both of'said signals,"first and second electrondise;

charge deviceseach-havinga screengrid cir-' cuitga controlgrid-circuit,""and ani'outputi circuity'means to "apply' alternatingvoltages m0? out or phase to "the control grid circuits of "saidelectron-- discharge devices "to alternately render both of saidelectron discharge devices to said transmission circuit, meansconnecting each of the output circuits of said first and secondoscillation generators to a respectively associated one of the screengrid circuits of said first and second electron discharge devices, andmeans connecting each of the input circuits of said first and secondoscillation generators to a respectively associated output circuit ofsaid electron discharge devices whereby said first oscillation generatoris operative and the signal produced thereby is relayed by one of saidelectron discharge devices to said transmission circuit only when theother of said electron discharge devices is inoperative, and said secondoscillation generator is operative and the signal produced thereby isrelayed by said other electron discharge device to said transmissioncircuit only when said one electron discharge device is inoperative.

4. In an electrical transmission system, first and second oscillationgenerators for producing separate electrical signals to be transmitted;each oscillation generator having an output circuit and an input circuitfor adjusting the oscillation generator to its oscillating andnon-oscillating condition, a common transmission circuit for both ofsaid signals, first and second electron discharge devices each having ascreen grid circuit, a control grid circuit, and an output circuit,means to apply alternating voltages 180 out of phase to the screen gridcircuits of said electron discharge devices to alternately render eachof the said electron devices inoperative, means connecting the outputcircuits of both of said electron discharge devices to said transmissioncircuit, means connecting each of the output circuits of said first andsecond oscillation generators to a respectively associated one of thecontrol grid circuits of said first and second electron dischargedevices, and means connecting each of the input circuits of said firstand second oscillation generators to a respectively associated outputcircuit of said electron discharge devices whereby said firstoscillation generator is operative and the signal produced thereby isrelayed by one of said electron discharge devices to said transmissioncircuit only when the other of said electron discharge devices isinoperative, and said second oscillation generator is operative and thesignal produced thereby is relayed by said other electron dischargedevice to said transmission circuit only when said one electron discharge device is inoperative.

5. In an electrical system including two oscillation generators eachhaving an output circuit and an input circuit for adjusting theoscillation generator to its oscillating and non-oscillating conditionin response to a keying signal, an electron discharge device having anoutput circuit and a pair of input circuits, means to impress a keyingsignal on one of said input circuits of said electron discharge deviceto produce an amplified keying signal in the output circuit of saidelectron discharge device, means connecting the output circuit of saidelectron discharge device to the input circuit of one of saidoscillation generators, and means connecting the output circuit of theother of said oscillation generators to the other input circuit of saidelectron discharge device for transmission of the applied oscillationsignal to a utilization circuit.

6. In an electrical system including two oscillation generators eachhaving an output circuit and an input circuit for adjusting theoscillation generator to its oscillating and non-oscillating conditionin response to a keying signal, an electron discharge device having ananode circuit, a screen grid circuit and a control grid circuit, meansto impress a keying signal on said control grid circuit of said electrondischarge device to produce an amplified keying signal in the anodecircuit of said electron discharge device, means connecting the anodecircuit of said electron discharge device to the input circuit of one ofsaid oscillation generators, and means connecting the output circuit ofthe other of said oscillation generators to the screen grid circuit ofsaid electron discharge device for transmission of the appliedoscillation signal to a utilization circu'it.

7. In an electrical system including two oscillation generators eachhaving an output circuit and an input circuit for adjusting theoscillation generator to its oscillating and non-oscillating conditionin response to a keying signal, an electron discharge device having ananode circuit, a screen grid circuit and a control grid circuit, meansto impress a keying signal on said screen grid circuit of said electrondischarge device to produce an amplified keying signal in the anodecircuit of said electron discharge device, means connecting the anodecircuit of said electron discharge device to the input circuit of one ofsaid oscillation generators, and means connecting the output circuit ofthe other of said oscillation generators to the control grid circuit ofsaid electron discharge device for transmission of the appliedoscillation signal to a utilization circuit.

RUDOLF F. WILD. FRED J. CURRAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

